1. Field of the Invention
The present invention relates to a modular method for manufacturing printed circuit boards, which is a method of manufacturing multilayer printed circuit boards with blind and buried vias structure by using basic components as the assembly units. The method adopts a dry film lamination method to press a dry film dielectric (i.e. a dielectric material in the form of a dry film, which is a semi-sticky plastic state) at B-stage (i.e. the stage of a resin before its reaching a glass conversion state) onto a laminate after the photolithography and etching processes are performed. Vias are drilled at appropriate positions on the upper and lower layers that require an electric connection, and then a plastic conductive material is filled into the vias to produce basic components. To comprise the basic components, circuit boards having blind vias and single-sided or double-sided circuits, the dielectric materials and the copper clads according to the required multilayer printed circuit board mode, then heating and pressurization process is performed once to form the multilayer printed circuit boards with blind and buried vias structure. Such arrangement not only saves the time for aligning layers, pressing and blind via filled plating of the prior-art technology, but also enhances the yield rate and reduces the failure cost.
2. Description of the Related Art
In the traditional printed circuit board manufacturing, the design of a single-sided or a double-sided inserted component and via is common at early stage. However, more and more functions are required for the electronic products and cause a demand for a high circuit density. The design of printed circuit boards tends to be a multilayer board design. The layout area is increased by having more layers of a printed circuit board, and the plating through hole (PTH) method is still adopted for electrically connecting the layers.
Since the plate through hole method for electrically connecting the layers will waste the layout real estate for the printed circuit board that does not need an electric connection between layers, therefore a high density interconnect (HDI) method by using a laser drilling method to electrically connect a layer with the next layer is adopted to overcome the aforementioned shortcoming. The high density interconnect method become a common method for manufacturing a multilayer circuit board that has a structure with blind vias (vias electrically interconnecting the outmost layer of the circuit board to the next layer or the layer next to the next layer) and buried vias (vias electrically interconnecting layers within the circuit board only, but not electrically interconnected to the outmost layer directly).
In the build up process by using the laser drilling method to produce blind vias layer by layer, a special chemical solution of a higher cost is used to fill plate the blind vias for long hours in order to stack the blind vias at the built up layer on the blind vias at the next layer (Stack Via) to save the real estate and increase the electric conduction reliability.
Please refer to FIGS. 1A to 1E for the illustrative views of the build up process and the flow of interconnecting the next layer according to a prior-art printed circuit board manufacturing technology. An electric circuit 110, 120 as shown in FIG. 1A is produced on a copper clad laminate 100 by photolithography and etching processes and a dielectric material 130 such as a resin-impregnated fiberglass fabric or a resin-impregnated short-fiber polyamide mat and copper clad 140 is deposited on the electric circuit 110 as shown in FIG. 1B. For laser drilling, carbon dioxide (CO2) laser is generally used, and such laser can effectively burn the resin polymer layer of a circuit board, but cannot burn the metal layer of a circuit board. Therefore, it is necessary to use a photoresist agent to protect the metal layer 140 and expose the section that requires an electrical interconnect, and then etch the metal of the section 150 (this process is commonly known as “Conformal Window” process) as shown in FIG. 1C. Then, drill a via 160 by laser drilling as shown in FIG. ID and plate a metal layer 170 on the sidewall of the via 160 as shown in FIG. 1E.
Please refer to FIGS. 2A to 2J for the illustrative views of the flow of producing an 8-layer printed circuit board having blind and buried vias structure according to a prior-art printed circuit board manufacturing technology.
An electric circuit 210, 220 as shown in FIGS. 2A and 2B is produced on a copper clad laminate 200 by photolithography and etching processes and a dielectric 230 such as a resin-impregnated fiberglass fabric or a resin-impregnated short-fiber polyamide mat and copper clad 240 is deposited on the electric circuit 210, 220 as shown in FIG. 2C, to perform a heating and pressurization process for a tight press as shown in FIG. 2D, and then perform mechanical drilling and plating operations to give an electrical connection function between the layers that require electrical interconnection. A conductive material 250 fills the vias by a silk screen printing method to allow stack via (blind vias stack on the buried vias) and increase the electric conduction reliability between new built-up layers. An electric circuit is produced on the outer layer by the photolithography and etching method. Therefore, the core 4-layer circuit structure of the 8-layer circuit board having blind and buried via structure is completed (as shown in FIG. 2E.)
And then, the build up process is carried out as follows:
A dielectric 230 and a metal clad 240 used for pressing are deposited on such a core 4-layer circuit structure (as shown in FIG. 2F), and the heating and pressurization process is performed once again for a tight press, and then the conformal window, laser drilling, via filled plating, photolithography and etching processes are performed to electrically connect the core 4-layer circuit structure and the new build up circuit layer to produce the blind via 260 and the electric circuit as shown in FIGS. 2G to 2H. Therefore, a core 6-layer circuit structure of the 8-layer circuit board having blind and buried via structure is completed.
Then, the build up process is performed once again.
A dielectric 230 and a metal clad 240 used for pressing are deposited on such a core 6-layer circuit structure, and the heating and pressurization process is performed for the third time for a tight press (as shown in FIG. 2I), and then the mechanical drilling, conformal window, laser drilling, via filled plating, photolithography and etching processes are performed to produce the blind via and the outermost electric circuit as shown in FIG. 2J. Therefore, an 8-layer circuit board having blind and buried vias is completed.
Similarly, a circuit board with more layers having the blind and buried via structure can be made by repeating the procedure above.
However, it is noteworthy that the plated metal can just be deposited along the sidewall of the via (as indicated by 170 in FIG. 1E) in traditional plating, and the blind via cannot be filled. Therefore, a special chemical solution of a very high cost is needed for the foregoing via filled plating to achieve the purpose of filling the via by plating.
Further, the prior-art technology requires a pressing process each time for adding a layer. Since each pressing can only confirms the alignment between a new circuit layer and its next circuit layer, therefore a serious deviation on the alignment between different circuit layers caused by the increased times of pressings will be resulted.
From the foregoing process, it is obvious that the prior-art process takes long time, not only is difficult to enhance the yield rate, but also increase the cost of fault at a later stage of the manufacturing process.